Kinetic and mechanistic study of OH- and Cl-initiated oxidation of two unsaturated HFCs: C4F9CH=CH2 and C6F13CH=CH2

Article abstract of DOI:10.1021/jp0013199

The kinetics and mechanisms of the OH- and Cl-initiated oxidation of two unsaturated HFCs, C₄F₉CH=CH₂ and C₆F₁₃CH=CH₂, were investigated. The kinetic study was performed as a function of pressure and temperature for the OH reactions and as a function of pressure at 298 K for Cl atom reactions. The rate constants obtained are (in units of cm³ molecule^-1 s-1): κ(OH + C₄F₉CH=CH₂) = (8.5 ±1.4) x 10^-13 exp[(139 ±48)/T] and κ(OH + C₆F13CH=CH₂) = (1.3 ±0.5) x 10-¹² exp[(31 ±124)/T] in the temperature range 233-372 K; and κ(Cl + C₄F₉CH=CH₂) = (8.9 ±1.0) x 10^-11 and κ(C1 + C₆F₁₃CH=CH₂) = (9.1 ± 1.0) x 10-11 at 298 K. The OH and Cl reactions rate constants were found to be independent of pressure in the range 10-760 and 15-60 Torr, respectively. The mechanistic study was performed in air at atmospheric pressure, in the presence or absence of NO_x. CO and COF₂ have been identified as the major secondary products of both OH- and Cl-initiated oxidation of the HFCs. However, there is evidence for the formation of different primary products: aldehydes (C₄F₉CHO and C₆F₁₃CHO) in the OH oxidation of the HFCs and ketones (C₄F₉C(O)CH₂C1 and C₆F₁₃C(O)CH₂Cl) in the Cl oxidation. This suggests that the oxy radicals, precursors of these carbonyl compounds, behave differently. The β-hydroxyoxy radicals C₄F₉CH(O)CH₂OH and C₆F₁₃CH(O)CH₂OH decompose, whereas the β-chlorooxy radicals C₄F₉CH(O)CH₂C1 and C₆F₁₃CH(O)CH₂C1 react with O₂. These results are consistent with the significantly higher activation barrier for the decomposition of the β-chlorooxy, compared to that of the β-hydroxyoxy radicals.

Full text of DOI:10.1021/jp0013199

8512
J. Phys. Chem. A 2000, 104, 8512-8520
Kinetic and Mechanistic Study of OH- and Cl-Initiated Oxidation of Two Unsaturated
HFCs: C4F9CHdCH2 and C6F13CHdCH2
E. Ve´sine, V. Bossoutrot, A. Mellouki,* G. Le Bras, J. Wenger,† and H. Sidebottom‡
LCSR/CNRS-1C, AVenue de la recherche scientifique, 45071, Orle´ans Cedex 2, France
ReceiVed: April 6, 2000; In Final Form: June 16, 2000
The kinetics and mechanisms of the OH- and Cl-initiated oxidation of two unsaturated HFCs, C4F9CHdCH2
and C6F13CHdCH2, were investigated. The kinetic study was performed as a function of pressure and
temperature for the OH reactions and as a function of pressure at 298 K for Cl atom reactions. The rate
constants obtained are (in units of cm3 molecule-1 s-1): k(OH + C4F9CHdCH2) ) (8.5 ( 1.4) × 10-13
exp[(139 ( 48)/T] and k(OH + C6F13CHdCH2) ) (1.3 ( 0.5) × 10-12 exp[(31 ( 124)/T] in the temperature
range 233-372 K; and k(Cl + C4F9CHdCH2) ) (8.9 ( 1.0) × 10-11 and k(Cl + C6F13CHdCH2) ) (9.1 (
1.0) × 10-11 at 298 K. The OH and Cl reactions rate constants were found to be independent of pressure in
the range 10-760 and 15-60 Torr, respectively. The mechanistic study was performed in air at atmospheric
pressure, in the presence or absence of NOx. CO and COF2 have been identified as the major secondary
products of both OH- and Cl-initiated oxidation of the HFCs. However, there is evidence for the formation
of different primary products: aldehydes (C4F9CHO and C6F13CHO) in the OH oxidation of the HFCs and
ketones (C4F9C(O)CH2Cl and C6F13C(O)CH2Cl) in the Cl oxidation. This suggests that the oxy radicals,
precursors of these carbonyl compounds, behave differently. The â-hydroxyoxy radicals C4F9CH(O)CH2OH
and C6F13CH(O)CH2OH decompose, whereas the â-chlorooxy radicals C4F9CH(O)CH2Cl and C6F13CH(O)-
CH2Cl react with O2. These results are consistent with the significantly higher activation barrier for the
decomposition of the â-chlorooxy, compared to that of the â-hydroxyoxy radicals.
Introduction
In this paper, we report the first kinetic and mechanistic study
of OH and Cl reactions with two unsaturated HFCs: C4F9CHd
CH2 and C6F13CHdCH2. The mechanistic studies were per-
formed in the presence and absence of NOx.
The legislated phase out of chlorofluorocarbons (CFCs) has
led to the use of substitutes, mainly hydrochlorofluorocarbons
(HCFCs) and hydrofluorocarbons (HFCs). These hydrogen-
containing compounds react with the OH radicals in the
troposphere by an H-atom transfer mechanism. The resulting
lower atmospheric lifetimes compared to the CFCs make these
compounds more acceptable as alternatives. HCFCs are less
efficient than CFCs in depleting stratospheric ozone. The effect
of these chlorine-containing molecules is, however, not totally
negligible and they are also planned to be phased out in the
near future. HFCs, which do not contain chlorine, have no effect
on stratospheric ozone but they strongly absorb infrared radiation
and they may then contribute to the greenhouse effect. The
global warming potential of a compound will depend on its
capacity to absorb infrared radiation in the atmospheric window
(770-1430 cm-1) and on its atmospheric lifetime. The overall
atmospheric impact of such compounds may also depend on
the fate and impact of their oxidation products. The tropospheric
chemistry of the saturated HFCs is mainly controlled by reaction
with OH radicals while for the unsaturated ones the contribution
of NO3 and O3 reactions might be not negligible. The oxidation
by Cl atoms is likely to be negligible, considering the presently
estimated low Cl atom concentration in the troposphere.
However, chlorine atom oxidation in laboratory experiments can
provide additional information which can help in defining the
atmospheric oxidation of HFC and other organic compounds.
Experimental Section
The rate constants for the reactions of OH radicals with the
two unsaturated HFCs have been measured using the pulsed
laser photolysis-laser-induced fluorescence (PLP-LIF) method.
The rate constants for reactions of Cl atoms have been
determined using pulsed laser photolysis-resonance fluores-
cence. The studies of the oxidation mechanisms were carried
out in a photoreactor coupled with FTIR analysis of the reactants
and products.
Pulsed Laser Photolysis-Laser-Induced Fluorescence
(PLP-LIF). The PLP-LIF technique and the methodology used
have been already described in detail previously (e.g., ref 1)
and is only briefly discussed here. Two sources were used to
generate OH radicals: photolysis of H2O2 at λ ) 248 nm (KrF
excimer laser) and photolysis of HONO at λ ) 351 nm (XeF
excimer laser). This has been done in order to check the possible
complications arising from the photolysis wavelength. The
concentration of OH radicals was monitored at various reaction
times ranging from 10 µs to 10 ms by pulsed LIF. A Nd:YAG-
pumped frequency-doubled dye laser was used to excite the OH
radicals at λ ) 282 nm. Fluorescence from the OH radicals
was detected by a photomultiplier fitted with a 309 nm narrow
band-pass filter. The integrated signals from 10 to 15 delay times
from 100 probe laser shots were averaged to generate OH
concentration-time profiles over at least three lifetimes.
* Corresponding author. E-mail: mellouki@cnrs-orleans.fr.
† Department of Chemistry, University College, Cork, Ireland.
‡ Department of Chemistry, University College, Dublin, Ireland.
10.1021/jp0013199 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/26/2000

OH- and Cl-Initiated Oxidation of Unsaturated HFCs
J. Phys. Chem. A, Vol. 104, No. 37, 2000 8513
TABLE 1: OH + C4F9CH)CH2 Reaction: Experimental
Pulsed Laser Photolysis-Resonance Fluorescence (PLP-
RF). This experimental setup as well as the methodology used
to measure chlorine atom reaction rate constants have also been
already described in previous papers from our group (e.g., ref
2). Briefly, chlorine atoms were produced by photolyzing Cl2
at 355 nm using a pulsed, frequency tripled, Nd:YAG laser
operated at 10 Hz. The radiation (λ ∼ 135 nm) from a
microwave discharge in a flowing mixture of (0.2-0.3%) Cl2/
helium at ∼2 Torr pressure was used to excite the fluorescence
of Cl atoms in the reactor. A solar blind photomultiplier tube
perpendicular to both the resonance lamp and photolysis laser
beam collected the resonance fluorescence radiation resulting
from excitation of Cl. Signals were obtained using photon-
counting techniques in conjunction with multichannel scaling.
The decay curves following 10 000-40 000 laser pulses were
co-added to improve the signal-to-noise ratio.
Conditions and Measured Rate Constants
T
P
[C4F9CHdCH2]
k′ - k′0
(s-1
(k ( 2σ) × 1012
(K) (Torr) (1014 molecules cm-3
)
)
(cm3 molecule-1 s-1
)
372 100
100
3.49-20.28
3.56-20.83
4.65-22.38
2.04-21.74
2.06-23.15
5.16-21.06
5.94-66.45
2.33-24.63
2.28-28.42
2.93-33.60
5.09-55.88
1-12.28
645-2736
726-2961
485-2818
467-2875
470-3086
660-2924
793-8475
626-3485
477-3804
549-4480
1206-7610
1419-3011
427-3973
715-4462
1085-4395
509-3808
436-5389
628-4930
1401-4348
1069-5875
725-6633
934-5469
1.27 ( 0.03
1.33 ( 0.16a
1.29 ( 0.10a
1.26 ( 0.03
1.27 ( 0.02
1.35 ( 0.09a
1.25 ( 0.06
1.31 ( 0.02
1.28 ( 0.01
1.30 ( 0.02
1.27 ( 0.02
1.25 ( 0.04
1.44 ( 0.06a
1.33 ( 0.10a
1.41 ( 0.07a
1.34 ( 0.02
1.46 ( 0.08a
1.43 ( 0.01
1.56 ( 0.04
1.55 ( 0.08a
1.54 ( 0.03
1.63 ( 0.09a
100
343 100
323 100
100
298 300
200
100
100
50
10
100
100
50
3.94-28.80
5.80-32.42
8.96-35.72
2.44-27.02
1.89-35.97
2.76-32.78
1.99-22.07
7.69-38.61
3.67-42
Photoreactor. Product studies were performed at UCD-
Dublin using the experimental setup described elsewhere.3
Reactions were carried out in FEP Teflon cylindrical reaction
vessel with a volume of about 50 L surrounded by 10 lamps
(Philips, TL 20W/09) with irradiation in the range 300-460
nm and a maximum intensity at 365 nm for photolysis of Cl2
to generate Cl atoms and 10 lamps (Philips, TUV 15W, λ )
254 nm) for photolysis of H2O2 to generate OH radicals.
Measured amounts of reagents were flushed from calibrated
bulbs into the Teflon bag by a stream of ultrapure air (Air
Liquide). The photoreactor was then filled to its full capacity
with ultrapure air. A Mattson Polaris FTIR spectrometer was
used for analysis. FTIR spectra were obtained by using an
evacuable 2 L Teflon-coated cell containing a multipass White
mirror arrangement which was mounted in the cavity of the
spectrometer. Spectra were recorded using a 6 m path length
over the wavelength range 500-4000 cm-1 with a resolution
of 2 cm-1. The spectra were derived from 64 co-added spectra.
273 100
100
253 100
20
100
233 100
100
7.19-40.03
a Experiments performed with HONO as source of OH.
Materials. Purities of the chemicals were as follows: helium,
the carrier gas (UHP certified to >99.9995% (Alphagaz)), was
passed from the tank to the cell through a liquid nitrogen trap;
Cl2 (99.8%, UCAR) was degassed several times at 77 K before
use; O2 was certified to >99.995% (Alphagaz). The 50 wt %
H2O2 solution obtained from Prolabo was concentrated by
bubbling helium through the solution to remove water for several
days prior to use, and constantly during the course of the
experiments. It was admitted into the reaction cell by passing a
small flow of helium through a glass bubbler containing H2O2.
HONO was produced in situ by reacting NaNO2 (0.1 M) with
dilute H2SO4 (10%) contained in a stirred round-bottomed flask.
The effluent from the flask was swept into the cell by a known
flow of helium. C4F9CHdCH2 and C6F13CHdCH2 were from
Elf Atochem and their purities were higher than 96.5% and 97%,
respectively. The analyzed impurities in the HFCs samples were
shown to consist of fluorinated alkanes.
Figure 1. Arrhenius expression of the rate constants for the reactions
of OH with C4F9CHdCH2 and C6F13CHdCH2.
of the HFC; it is the sum of the reaction rate of OH with its
precursor (H2O2 or HONO, with concentrations in the range
(2-10) × 1013 molecules cm-3), and the diffusion rate of OH
out of the detection zone. k′0 was typically around 100 s-1
.
Results and Discussion
Reaction OH + C4F9CHdCH2. The reaction of OH with
C4F9CHdCH2 was studied over the temperature range 233-
372 K using H2O2 or HONO as the OH source. The obtained
data were similar with the two sources as shown in Table 1
and Figure 1.
The experiments were performed in the pressure ranges 10-
300 Torr at 298 K and 20-100 Torr at 253 K. No pressure
dependence of the reaction rate constant was observed in these
ranges. Changes in the experimental conditions (photolysis laser
fluence by a factor of 2, and flow velocity by a factor of 3) did
not affect the obtained data. The Arrhenius expression derived
from the unweighted least-squares fit to the combined results
Kinetic Studies. OH Reaction Rate Constant Measurements.
Reactions were studied under pseudo-first-order conditions with
the OH concentration much lower than that of the HFCs ([OH]0
) (0.2-2) × 1011 molecules cm-3). Thus, the OH concentration
time profile followed the pseudo-first-order rate law:
[OH]t ) [OH]0e-k′t
; k′ ) k[HFC] + k′0
where k is the rate coefficient for the reaction OH + HFC. The
decay rate, k′0, is the first-order OH decay rate in the absence

8514 J. Phys. Chem. A, Vol. 104, No. 37, 2000
Ve´sine et al.
TABLE 2: OH + C6F13CH)CH2 Reaction: Experimental
TABLE 3: Experimental Conditions and the Measured Rate
Constant Data for the Cl Reaction with C4F9CH)CH2 and
C6F13CH)CH2
Conditions and Measured Rate Constants
T
P
[C6F13CHdCH2]
k′ - k′0
(s-1
(k ( 2σ) × 1012
P
[HFC] × 10-12
k′ - k′0
(s-1
k × 1011
(K) (Torr) (1014 molecules cm-3
)
)
(cm3 molecule-1 s-1
)
molecule
(Torr) (molecules cm-3
)
)
(cm3 molecule-1 s-1
)
372 100
100
348 100
333 100
323 100
298 760
400
0.7-8.72
105-1178
115-1315
105-1267
119-1514
106-1380
1020-5056
180-2506
138-2293
65-1345
111-1353
111-1232
104-1137
122-672
129-1321
125-1130
130-1259
167-1482
83-1261
134-1906
121-1573
233-2203
137-1742
207-1773
1.36 ( 0.05
1.50 ( 0.09
1.38 ( 0.03
1.44 ( 0.06
1.38 ( 0.04
1.35 ( 0.11
1.22 ( 0.05
1.18 ( 0.04
1.50 ( 0.03
1.42 ( 0.06
1.61 ( 0.08
1.33 ( 0.03
1.36 ( 0.14
1.65 ( 0.10a
1.73 ( 0.18a
1.51 ( 0.07a
1.61 ( 0.08a
1.70 ( 0.11a
1.44 ( 0.04
1.63 ( 0.06
1.45 ( 0.07
1.47 ( 0.18
1.40 ( 0.04
C4F9CHdCH2
60
15
60
15
6.0-53.3
4.7-49.0
6.9-65.11
4.1-47.02
542-4437
392-3890
606-5867
365-3948
8.9 ( 1.0
9.1 ( 1.0
0.93-8.95
0.69-9.31
1.06-10.65
0.78-10.05
8.28-37.31
1.77-20.93
1.35-19.76
0.84-8.91
0.83-9.80
0.69-7.50
0.62-8.59
0.36-5.07
0.74-8.07
0.64-7.09
0.82-8.62
1.01-9.38
0.65-7.83
0.94-14.61
0.91-9.64
1.47-16.53
1-10.90
C6F13CHdCH2
Discussion. The present rate constant data are the first to be
reported for OH reactions with long-chain fluoroalkenes.
However, these results can be compared with the existing data
on the OH reactions with smaller fluoroalkenes such as
fluoroethenes and fluoropropenes. Recently, Orkin and al.4
reported rate constants data for the reaction of OH with CF3-
CHdCH2, CF3CFdCH2, and CF3CFdCF2. Their data showed
that the reaction of OH with CF3CHdCH2 (1.5 × 10-12 cm3
molecule-1 s-1) is more than 1 order of magnitude slower at
298 K than the reaction of OH with CH3CHdCH2 (26.3 × 10-12
cm3 molecule-1 s-1). This was attributed to the presence of the
strongly electron-withdrawing CF3- group. Our data shows that
the substitution of CF3- by the larger fluorinated groups C4F9-
or C6F13- does not lead to a significant change in the rate
constants at 298 K (k ) 1.5 × 10-12, 1.3 × 10-12, 1.5 × 10-12
cm3 molecule-1 s-1 for CF3CHdCH2, C4F9CHdCH2, and C6F13-
CHdCH2, respectively). These C4F9- and C6F13- groups have
essentially the same deactivating effect as CF3-. In a manner
similar to the simple alkenes, the reactions of OH with
fluorenated alkenes have a small negative temperature factor,
E/R, which is consistent with an addition of OH to the double
bond of the alkenes. However, it is interesting to note that the
E/R factor for OH reaction with CH3CHdCH2 (-504 K) is
lower than that with CF3CHdCH2, C4F9CHdCH2, and C6F13-
CHdCH2 (-183, -139, and -31 K, respectively).
300
100
100
100
50
20
100
100
100
100
100
273 100
100
253 100
100
100
1.22-12.81
a Experiments performed in the presence of O2.
obtained with the two OH sources in the temperature range
233-372 K is
k(OH+C4F9CHdCH2) )
(8.5 ( 1.4) × 10-13 exp[(139 ( 48)/T] cm3 molecule-1 s-1
The uncertainties for the preexponential factor, A, and the
activation energy are given by ∆A ) 2AσlnA and ∆E/R ) 2σE/R
The room temperature rate constant taken as the average of
all values obtained at 298 K is
.
Cl Reaction Rate Constant Measurements. The chlorine
atom reactions with the two HFCs were also studied under
pseudo-first-order conditions with the Cl concentration much
lower than that of the HFCs. Thus, the Cl concentration time
profile followed the pseudo-first-order rate law:
k(OH+C4F9CHdCH2) )
(1.3 ( 0.2) × 10-12 cm3 molecule-1 s-1
[Cl]t ) [Cl]0e-k′t
; where k′ ) k[HFC] + k′0
The uncertainty represents the statistical one to which we have
added 10% for systematic errors.
Reaction OH + C6F13CHdCH2. The rate constant for this
reaction was determined over the temperature range 253-372
K using H2O2 as the OH source (Table 2).
k is the rate coefficient for the reaction of Cl with HFC. The
decay rate, k′0, is the first-order Cl decay rate in the absence of
the HFC; it is the diffusion rate of Cl out of the detection zone.
The measurements were performed at 298 ( 2 K and at two
different pressures, 15 and 60 Torr of helium. The obtained rate
constants are
At 298 K, measurements were carried out in the pressure
range 20-760 Torr. Several experiments were also performed
in the presence of O2 (PO ) 3-7 Torr) at 100 Torr. At 298 K,
2
the data obtained at different pressures and in the presence or
absence of O2 were similar. The following value
k(Cl+C4F9CHdCH2) )
(8.9 ( 1.0) × 10-11 cm3 molecule-1 s-1
k(OH+C6F13CHdCH2) )
k(Cl+C6F13CHdCH2) )
(1.5 ( 0.3) × 10-12 cm3 molecule-1 s-1
(9.1 ( 1.0) × 10-11 cm3 molecule-1 s-1
represents the average of the combined data obtained at room
temperature. The measured rate constants are shown plotted in
Arrhenius form in Figure 1. The Arrhenius expression derived
from the experimental data between 253 and 372 K is
independent of pressure between 15 and 60 Torr. The
experimental conditions together with the values of the rate
constants are presented in Table 3, and shown in Figure 2.
Discussion. Rate constants k(Cl+C4F9CHdCH2) and
k(Cl+C6F13CHdCH2) are equal within the experimental errors.
Comparison of the rate constant data for the reactions of Cl
atoms with the unsaturated HFCs determined in this work, with
the reported rate constant of reaction Cl + CH3CHdCH2 (k)
2 × 10-10 cm3 molecule-1 s-1 at 298 K for the addition
channel),5 indicates that the C4F9- and C6F13- groups have a
k(OH+C6F13CHdCH2) )
(1.3 ( 0.5) × 10-12 exp[(31 ( 124)/T] cm3 molecule-1 s-1
Uncertainties are calculated similarly to that for k(OH+C4F9-
CHdCH2).

OH- and Cl-Initiated Oxidation of Unsaturated HFCs
J. Phys. Chem. A, Vol. 104, No. 37, 2000 8515
showed that photolysis at 254 or 365 nm contributed to less
than 1% per hour in the consumption of the two HFCs.
Mechanism of the OH-Initiated Oxidation of C4F9CHdCH2.
(a) In the Absence of NOx. Experiments were performed by
irradiation of C4F9CHdCH2/H2O2/air mixtures at 254 nm. Five
independent experiments were conducted where the initial
concentrations of C4F9CHdCH2 were in the range 20-90 ppm.
An example of obtained FTIR spectra before irradiation and
after 60 min of irradiation of the mixture is given in Figure 3.
The identified reaction products were CO, COF2, and HC-
(O)OH. In addition, after subtraction of the spectra of the
products CO, COF2, and HC(O)OH, and also C4F9CHdCH2,
an absorption band between 1830 and 1730 cm-1 was observed
and attributed to the carbonyl function (CdO) of C4F9C(O)H
similarly to that of C6F13C(O)H which has been produced in
an independent experiment by the photolysis of a mixture of
C6F13CHdCH2/Cl2/air (see next section). The residual spectrum
also shows a series of bands between 1400 and 1100 cm-1 which
correspond to C-F bonds of C4F9.
The observed plots of CO, COF2, and C4F9C(O)H concentra-
tions versus C4F9CHdCH2 consumed (Figure 4) indicate that
CO and COF2 are secondary products while the fluorinated
aldehyde is a primary product of the reaction. A primary product
is defined as a product whose formation is rate limited by the
initial OH reaction with the HFCs, while for a secondary
product, the formation is rate limited by the reaction of a primary
product.
The following mechanism is suggested to explain these
observations. The primary step of the OH reaction with C4F9-
CHdCH2 is an electrophilic addition of OH to the double bond
and predominantly to the terminal carbon. The yield of this
addition channel is expected to be higher than 65% which is
the yield of the similar channel of the OH + propene addition
reaction.6 This hypothesis is based on the strong electron-
Figure 2. Reactions of Cl with C4F9CHdCH2 and C6F13CHdCH2:
plots of (k′ - k′0) versus C4F9CHdCH2 and C6F13CHdCH2 concentra-
tions at 298 K.
significant deactivation effect with respect to reaction with Cl
atoms as observed for the OH reactions but lower. The
deactivation effect is not as pronounced as for the analogous
reactions with OH radicals. This is the consequence that
reactions of Cl atoms are much faster and then have a much
narrower range of rate constants than the OH reactions.
Mechanistic Studies. The oxidation of the two unsaturated
HFCs was initiated by either OH radicals or Cl atoms in air in
the absence or presence of NOx. Preliminary experiments
Figure 3. FTIR spectra for the OH + C4F9CHdCH2 reaction in air in the absence of NOx: (a) spectrum of C4F9CHdCH2 before irradiation, (b)
spectrum after 60 min irradiation, (c) spectrum of C4F9C(O)H after subtraction of C4F9CHdCH2,COF2, CO and HC(O)OH, and (d) reference
spectrum of COF2. Absorbance is in arbitrary units.

8516 J. Phys. Chem. A, Vol. 104, No. 37, 2000
Ve´sine et al.
However, HCHO was not observed since it reacted rapidly with
OH. The absolute concentrations of CO and COF2 were
determined using their calibrated reference spectra. This was
not possible for C4F9C(O)H since its calibrated spectrum was
not available. Accounting only for CO, COF2, and HC(O)OH
as reaction products the carbon balance is about 43%. The
missing part could be attributed mainly to C4F9C(O)H. The
observed CO and HC(O)OH products are expected to be
generated from the oxidation of HCHO.7 COF2 is likely to be
produced from the aldehyde C4F9C(O)H which reacts with OH
or photolyses to form C4F9 which is a precursor of COF2:
C4F9C(O)H + OH f C4F9CO + H2O
C4F9C(O)H + hν f C4F9 + products
C4F9CO + O2 + M f C4F9C(O)O2 + M
C4F9CO + M f C4F9 + CO + M
(8a)
(8b)
(9)
(10)
C4F9C(O)O2 + C4F9C(O)O2 f 2C4F9C(O)O + O2 (11)
Figure 4. Concentrations of products versus consumption of C4F9-
CHdCH2 in the OH-oxidation of C4F9CHdCH2 in the absence of NOx,
in air, [C4F9CHdCH2]o )30 ppm.
C4F9C(O)O + M f C4F9 + CO2 + M
C4F9 + O2 + M f C4F9O2 + M
C4F9O2 + RO2 f C4F9O + products
C4F9O + M f C3F7 + COF2 + M
C3F7 + O2 + M f f f COF2
(12)
(13)
(14)
(15)
(16)
withdrawing effect of the C4F9 group which is expected to
reduce the electron density on the adjacent carbon of the double
bond in C4F9CHdCH2 more than that of the terminal carbon.
Therefore, in air, the following initial mechanism is expected:
OH + C4F9CHdCH2 + M f C4F9CHCH2OH + M (1)
C4F9CHCH2OH + O2 + M f C4F9CH(OO)CH2OH + M
CF3O produced in sequence (16) may partly react with the
peroxy radicals CnF2n+1O2 to produce trioxide CF3O3CnF2n+1
since IR bands characteristics of trioxide were probably
observed.8,9 This mechanism, where COF2 is formed through
the C4F9C(O)H intermediate, is consistent with the observation
of COF2 as a secondary product.
The relative importance of reactions 8a and 8b in our
experiments is not known. However, photolysis of C4F9CHO
is likely to be slow at the 254 nm wavelength, considering the
low absorption cross section of the similar molecule, CF3CHO,
at this wavelength.10 The reaction of C4F9CHO with OH can
be significant within the reaction time of the experiment since
the concentration-time profile of C4F9CHO exhibits a maxi-
mum (observed after 1 h of experiment). The rate constant for
the reaction of C4F9CHO with OH (reaction 8a) is not known
but it can be assumed to be equal or less than that for the reaction
of CF3CHO with OH: k ) 6 × 10-13 cm3 molecule-1 s-1 at
298 K.11 This lower value compared to that for the initial
reaction of C4F9CHdCH2 with OH can qualitatively explain
the concentration-time profiles of C4F9CHO.
(b) In the Presence of NOx. Four experiments were performed
in the presence of NOx with initial concentrations of C4F9CHd
CH2 and NO ranging from 20 to 60 ppm and 15 to 45 ppm,
respectively. The major identified products were COF2 and CO.
Subtraction of the known spectra of C4F9CHdCH2, HC(O)-
OH, and COF2 from that obtained after 60 min of irradiation
gives a spectrum which indicates the presence of organic
nitrate(s) (Figure 5). This latter spectrum clearly shows the
characteristics of PAN-like absorption bands at 1841, 1741,
1304, and 790 cm-1. The PAN-like compound is most likely
C4F9C(O)O2NO2 produced from the reaction of C4F9C(O)H with
OH which has been suggested to be the major loss process for
(2)
In absence of NOx, the self-combination peroxy radical produced
can proceed through the two following channels:
C4F9CH(OO)CH2OH + C4F9CH(OO)CH2OH f
2C4F9CH(O)CH2OH + O2 (3a)
f C4F9C(O)CH2OH + C4F9CH(OH)CH2OH + O2 (3b)
The oxy radical formed in reaction 3a can decompose by
carbon-carbon bond fission or react with O2:
C4F9CH(O)CH2OH + M f C4F9C(O)H + CH2OH + M
(4)
C4F9CH(O)CH2OH + O2 f C4F9C(O)CH2OH + HO2 (5)
The observation of C4F9C(O)H and not that of C4F9C(O)CH2-
OH indicates that the reaction proceeds through channel 3a
followed by channel 4. The other possible decomposition
channel:
C4F9CH(O)CH2OH + M f C4F9 + HC(O)CH2OH + M
(6)
was considered to be unimportant since features corresponding
to a pure spectrum of glycolaldehyde, HC(O)CH2OH, was not
observed in the FTIR spectrum of the products. The CH2OH
radical also formed in reaction 4 will react with O2 to produce
HCHO:
CH2OH + O2 f HCHO + HO2
(7)

OH- and Cl-Initiated Oxidation of Unsaturated HFCs
J. Phys. Chem. A, Vol. 104, No. 37, 2000 8517
Figure 5. (a) Reference spectrum of PAN; (b) residual spectrum for the OH + C4F9CHdCH2 reaction in air, in the presence of NOx, obtained after
60 min photolysis, after subtraction of C4F9CHdCH2, HC(O)OH, and COF2.
C4F9C(O)H in our experiments. C4F9C(O)O2NO2 would be
produced by reactions 8a, 9, and 17:
C4F9C(O)O2 + NO2 + M f C4F9C(O)O2NO2 + M (17)
In the presence of NOx, C4F9C(O)H is also produced by
decomposition of the oxy radical C4F9CH(O)CH2OH (reaction
4). But this oxy radical is produced by the following reaction,
instead of reaction 3 in the absence of NOx:
C4F9CH(OO)CH2OH + NO f C4F9CH(O)CH2OH + NO2
(18)
Besides, the absorption band observed at 1764 cm-1 (Figure 5)
is likely due to an organic nitrate product like CnF2n+1O2NO2,
this band having been attributed to CF3O2NO2 in previous
studies.12,13
Mechanism of the Cl-Initiated Oxidation of C4F9CHdCH2.
(a) In the Absence of NOx. Two experiments were conducted
with initial concentrations of 40 ppm of the HFC and Cl2 in air
using the TL 20W/09 lamps (irradiation in the range 300-460
nm with a maximum intensity at 365 nm). CO, COF2, and an
Figure 6. Concentrations of products versus consumption of C4F9-
CHdCH2 in the Cl oxidation of C4F9CHdCH2 in air, in the absence
unknown species were observed. The obtained concentration
profiles of the products versus consumed C4F9CHdCH2 are
shown in Figure 6. The profiles indicate that CO and COF2 are
secondary products of the reaction as for the OH-initiated
oxidation of C4F9CHdCH2 while the “unknown” species is a
primary product.
of NOx. [C4F9CHdCH2]0 ) 40 ppm.
oxidation of C4F9CHdCH2 is assumed to be a C4F9-containing
carbonyl compound other than C4F9C(O)H.
The following mechanism is proposed to explain the observed
products. For the same reason as for the OH reaction, the initial
addition channel is expected to occur predominantly at the
terminal carbon of the double bond:
The unknown product has an infrared band at 1788 cm-1
,
which corresponds to a carbonyl group. However, the corre-
sponding compound is not C4F9C(O)H, since the band at 1777
cm-1 attributed to this species in the OH-initiated oxidation of
C4F9CHdCH2 was not observed in the Cl-initiated oxidation.
Besides, the spectra obtained, after subtraction of C4F9CHd
Cl + C4F9CHdCH2 + M f C4F9CHCH2Cl + M (19)
The peroxy and oxy radical are produced as follows:
CH2 and COF2, show features in the region 1400-1100 cm-1
,
likely due to C-F absorption bands similar to those attributed
C4F9CHCH2Cl + O2 + M f C4F9CH(OO)CH2Cl + M
to C4F9C(O)H. Then, the unknown product in the Cl-initiated
(20)

8518 J. Phys. Chem. A, Vol. 104, No. 37, 2000
C4F9CH(OO)CH2Cl + C4F9CH(OO)CH2Cl f
Ve´sine et al.
2C4F9CH(O)CH2Cl + O2 (21)
The decomposition of the oxy radical, as observed in the OH
reaction
C4F9CH(O)CH2Cl + M f C4F9C(O)H + CH2Cl + M (22)
is unlikely since C4F9C(O)H, has not been observed in the Cl
+ C4F9CHdCH2 system. Therefore, the oxy radical most likely
reacts with O2:
C4F9CH(O)CH2Cl + O2 f C4F9C(O)CH2Cl + HO2 (23)
Some experiments carried out in pure oxygen did not show any
difference in the product distribution and yields. This supports
the assumption that oxy radicals predominantly react with O2
in air.
Then, the unknown carbonyl compound detected by FTIR
would be the ketone C4F9C(O)CH2Cl.
The present results show evidence for a difference in the
behavior of â-hydroxyoxy-C4F9CH(O)CH2OH, and â-chloro-
oxy-C4F9CH(O)CH2Cl radicals. The first one would predomi-
nantly decompose whereas the second one would react with
O2. A similar behavior has already been observed for the
HOCH2CH2O and ClCH2CH2O radicals produced in the OH-
and Cl-initiated oxidation of ethene in air, respectively. The
different behavior of HOCH2CH2O and ClCH2CH2O radicals
was consistent with the higher activation barrier for decomposi-
tion of ClCH2CH2O, 15-16 kcal mol-1, compared to that of
Figure 7. Concentration of product versus consumption of C6F13CHd
CH2 in the OH oxidation of C6F13CHdCH2 in air, in the absence of
NOx, [C6F13CHdCH2]0 ) 71 ppm.
those of HFC, COF2, and NOCl (formed through Cl + NO
(+M) f ClNO (+M)) from the spectrum obtained after 60 min
of irradiation time exhibit bands corresponding to PAN-like
compound(s) (i.e., 1841, 1741, 1304, and 1163 cm-1) as
observed for the OH-initiated oxidation of C4F9CHdCH2 in the
presence of NOx.
Mechanism of the OH-Initiated Oxidation of C6F13CHd
CH2. As for C4F9CHdCH2, the oxidation of C6F13CHdCH2
was initiated either by OH or Cl in the presence and absence of
NOx. The study of C6F13CHdCH2 is not described in detail since
its oxidation mechanisms are very similar to those of C4F9CHd
CH2.
(a) In the Absence of NOx. Two experiments were performed
with 50 and 71 ppm of C6F13CHdCH2. The resulting concen-
tration profiles of the reaction products versus consumed C6F13-
CHdCH2 are shown in Figure 7. In addition to CO, COF2, and
HC(O)OH, the fluorinated aldehyde (C6F13CHO) was observed.
This latter was identified by comparison with the IR spectra
obtained from the reaction of Cl with C6F13CH2OH in air which
was shown to produce C6F13CHO with a yield close to 100%
in this laboratory. The spectra of C6F13CHO were recorded from
an independent experiment after 2 min irradiation of a mixture
of 93 ppm of C6F13CH2OH and 96 ppm of Cl2 in air. In Figure
8 are shown the spectrum of C6F13CH2OH (a), the spectrum
obtained after 2 min irradiation of C6F13CH2OH/Cl2/air mixture
(b), and the spectrum (c) resulting from subtraction of C6F13-
CH2OH and COF2 from spectrum (b). The spectrum (c) is then
that of C6F13CHO. The spectra assigned to C6F13CHO and C4F9-
CHO obtained in reactions OH + C6F13CHdCH2 and OH +
C4F9CHdCH2, respectively, are presented in (d) and (e). Spectra
in (c), (d), and (e) show that the position of the absorption band
centered at 1778 cm-1, due to the CdO group of the aldehyde
is not affected by the number of the surrounding C-F bonds
(C4F9 or C6F13).
HOCH2CH2O, 10-11 kcal mol-1 14
A comparable difference
.
in the activation barrier for decomposition of ClCH2CH(O)-
CH3 and OHCH2CH(O)CH3 has been obtained from quantum
calculations for ClCH2CH(O)CH3 and HOCH2CH(O)CH3.16
15
Current quantum calculations from our laboratory for ClCH2-
CH(O)CF3 and HOCH2CH(O)CF3 lead to the same conclusion.15
Therefore, similar difference in the activation barriers for
decomposition of the C4F9CH(O)CH2Cl and C4F9CH(O)CH2-
OH oxy radicals is expected. This difference can explain the
mechanism suggested in this work, i.e., decomposition of
HOCH2CH(O)CF3 and reaction of ClCH2CH(O)CF3 with O2.
Concerning the ketone C4F9C(O)CH2Cl produced in reaction
23, the two potential loss processes are photolysis and reaction
with Cl. Photolysis is certainly negligible since photolysis of
another chloroketone, chloroacetone, CH3C(O)CH2Cl, has been
found to be negligible under the same experimental conditions
as those used for the study of the Cl oxidation of C4F9CHd
CH2. Then, the Cl reaction is likely to be the major loss process
of C4F9C(O)CH2Cl. But the observed profiles of product
concentration versus C4F9CHdCH2 consumed, specially the
delay in producing significant CO and COF2 end products,
indicates that the ketone is quite unreactive. Considering the
existing rate constant data for Cl reaction with acetone and
chloroacetone (k ) (3.1 ( 0.4) × 10-12 and k ) (3.5 ( 0.4) ×
10-12 cm3 molecule-1 s-1 at 298 K),17 the expected rate constant
for the Cl reaction with C4F9C(O)CH2Cl should be not higher
than 2 × 10-12 cm3 molecule-1 s-1. The value of this rate
constant will be in any case much lower than that of the initial
reaction of Cl with C4F9CHdCH2 (k ) (8.9 ( 0.6) × 10-11
cm3 molecule-1 s-1) and this can explain the observed product
profiles.
The profiles shown in Figure 7 indicate that C6F13CHO is a
primary product of the reaction while CO and COF2 are
secondary products as observed for C4F9CHdCH2. The overall
oxidation mechanism of C6F13CHdCH2 is expected to be similar
to that for C4F9CHdCH2.
(b) In the Presence of NOx. Two experiments were performed
with the following initial concentrations: [HFC]0 ) 20 and 40
ppm, [Cl2]0 ) 75 and 100 ppm, and [NO]0 ) 50 and 150 ppm,
respectively. The residual spectra obtained after subtraction of

OH- and Cl-Initiated Oxidation of Unsaturated HFCs
J. Phys. Chem. A, Vol. 104, No. 37, 2000 8519
Figure 8. FTIR spectra for the Cl + C6F13CH2OH reaction in air, in the absence of NOx: (a) spectrum of C6F13CH2OH before irradiation, (b)
spectrum after 2 min irradiation, (c) spectrum of C6F13CHO after subtraction of C6F13CH2OH and COF2, (d) spectrum of C6F13CHO from the OH
+ C6F13CHdCH2 reaction, and (e) spectrum of C4F9CHO from the OH + C4F9CHdCH2 reaction.
profiles of CO and COF2 behave like that of secondary products,
and the spectrum of the intermediate product differs slightly
from that of the fluorinated aldehyde (C6F13CHO).
One experiment was conducted in pure O2 ([C6F13CHdCH2]0
) 32 ppm, [Cl2]0 ) 60 ppm). The resulting profiles of the
products were similar to that in air, indicating that the nature
of the products and their yields do not depend on the concentra-
tion of O2. This suggests, similarly to the Cl + C4F9CHdCH2
mechanism, that the oxy radical C6F13CH(O)CH2Cl expected
to be formed reacts predominantly with O2, the decomposition
being negligible. The expected reaction product is the ketone,
C6F13C(O)CH2Cl, corresponding to the unknown carbonyl
infrared band observed.
(b) In the Presence of NOx. A single experiment was
conducted where the initial concentrations of C6F13CHdCH2,
Cl2, and NO were 31, 90, and 60 ppm, respectively. The reaction
product profiles (CO, COF2, and an unknown product with a
band at 1788 cm-1) are similar to those obtained with C4F9-
CHdCH2.
Conclusion
Figure 9. Concentrations of products versus consumption of C6F13-
CHdCH2 in the Cl oxidation of C6F13CHdCH2 in air, in the absence
of NOx, [C6F13CHdCH2]0 ) 30 ppm.
The results from this work provide some additional informa-
tion concerning the behavior of â-hydroxy-oxy and â-chloro-
oxy radicals, produced in OH and Cl oxidation of alkenes in
air. The obtained results suggest that the C4F9CH(O)CH2OH
(and C6F13CH(O)CH2OH) oxy radicals will decompose, whereas
the C4F9CH(O)CH2Cl (and C6F13CH(O)CH2Cl) oxy radicals will
react with O2 under air conditions. Such a different behavior of
â-hydroxyoxy and â-chlorooxy radicals, previously observed
for HOCH2CH2O and ClCH2CH2O,14 can be explained by a
significantly higher activation barrier for decomposition of the
â-chlorooxy compared to that for the decomposition of the
â-hydroxyoxy radicals. This different behavior leads to different
oxidation products since aldehydes will be produced in the OH
oxidation and ketones in the Cl oxidation of alkenes (except
ethene). This will have atmospheric implications if both OH
and Cl oxidation of alkenes occur in the atmosphere.
(b) In the Presence of NOx. Two experiments were conducted
with the initial concentrations [C6F13CHdCH2]0 ) 50 and 71
ppm, and [NO]0 ) 25 and 140 ppm, respectively. CO, HC(O)-
OH, and COF2 were identified as products. Characteristic bands
of a PAN-like compound were also observed, as in the OH +
C4F9CHdCH2 experiments in the presence of NOx.
Mechanism of the Cl-Initiated Oxidation of C6F13CHdCH2.
(a) In the Absence of NOx. Two experiments were performed
with the initial concentrations [C6F13CHdCH2]0 ) 15 and 30
ppm, and [Cl2]0 ) 150 and 30 ppm, respectively. The profiles
of the reaction products versus C6F13CHdCH2 consumed are
shown in Figure 9. As in the C4F9CHdCH2 experiments, the

8520 J. Phys. Chem. A, Vol. 104, No. 37, 2000
Ve´sine et al.
Concerning the atmospheric implications of this work, the
obtained results provide some information about the atmospheric
fate and impact of the studied HFCs if such compounds would
be used for industrial applications and released to the atmo-
sphere. Although the rate constants of the Cl reactions with the
studied HFCs are about 60 times higher than that of the OH
reactions, the OH reaction is very likely to be predominant in
the atmosphere, considering the assumed [Cl]/[OH] atmospheric
ratio (typically 103 cm-3/106 cm-3 ≈ 10-3). Therefore, the
atmospheric lifetimes of C4F9CHdCH2 and C6F13CHdCH2
would be around 8 days. This low lifetime first implies that
these HFCs would have a negligible greenhouse effect although
they strongly absorb infrared radiation in the atmospheric
window, as all the fluorine-containing hydrocarbons. Then the
rather short-lived C4F9CHdCH2 and C6F13CHdCH2 could have
a local or regional impact. Since they would be oxidized under
“rich” NOx conditions, they can produce ozone. Their ozone-
forming potential will depend on the fate of the intermediate
carbonyl compound, C4F9CHO and C6F13CHO, which is still
poorly known. The rates of their OH reaction and photolysis
need to be determined. The fate of these carbonyl compounds
will also influence the fluorinated product distribution and
impact. The OH reaction may lead to stable PAN type
compounds (C4F9C(O)O2NO2 and C6F13C(O)O2NO2) while
photolysis is likely to produce COF2 molecules by oxidation of
the C4F9 and C6F13 photofragments.
References and Notes
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Acknowledgment. We thank Elf Atochem Co. and Conseil
Re´gional du Centre for providing research grants to E.V.
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